Dual Apodization Filters for Vignetting Control in Optical Systems
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Solution Overview
Problem
Existing image pickup optical systems face challenges in forming a desired blurred image across all capturing areas due to vignetting, which affects the light distribution and results in uneven imaging performance, particularly for off-axis light beams.
Innovation Solution
The implementation of an image pickup optical system with a first and second apodization filter disposed on either side of the aperture stop, ensuring that the transmittance at one distance from the optical axis is greater than or equal to the transmittance at another distance, to control the light quantity distribution and achieve symmetrical pupil transmittance distributions for both on-axis and off-axis light beams.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a single apodization filter is disposed near the aperture stop to provide symmetrical transmittance distribution, then the on-axis light beam achieves proper light distribution, but the off-axis light beam suffers from vignetting and cannot achieve the desired effect
Solution Approach 1:
The single apodization filter is divided into two separate filters disposed on opposite sides of the aperture stop. The first apodization filter is located on the object side of the aperture stop, and the second apodization filter is located on the image side. This segmentation allows each filter to independently control light transmission for different angular ranges, with the first filter primarily affecting on-axis light beams and the second filter primarily affecting off-axis light beams, thereby resolving the vignetting issue while maintaining symmetrical transmittance distribution
Solution Approach 2:
Each apodization filter is designed with specific transmittance characteristics tailored to its position relative to the aperture stop. The first apodization filter has transmittance characteristics optimized for on-axis light beams, while the second apodization filter has transmittance characteristics optimized for off-axis light beams. This local optimization ensures that each region of the optical system receives the appropriate light distribution control for its specific angular characteristics
2Weight of stationary object
If the optical system is made smaller and lighter, then portability is improved, but vignetting becomes more difficult to eliminate completely
Solution Approach 1:
The invention accepts the presence of vignetting in compact optical systems and converts it into a beneficial effect. By strategically placing apodization filters on both sides of the aperture stop, the system uses the vignetting-induced asymmetric light paths to its advantage. The first apodization filter compensates for the reduced light transmission of on-axis beams, while the second filter compensates for off-axis beams, thereby achieving uniform light distribution across all angles of view even in a compact, vignetting-prone design
3Volume of moving object
If the aperture stop is designed to allow compact structure, then the optical system size is reduced, but the passing area for off-axis light beams becomes narrower compared to on-axis light beams
Solution Approach 1:
The invention addresses the reduced passing area in the lateral dimension by introducing a temporal dimension - placing apodization filters at two different positions along the optical axis (before and after the aperture stop). This allows the system to control light transmission in the axial dimension, compensating for the lateral dimension constraints imposed by vignetting. The dual-filter configuration enables proper light distribution despite the narrowed off-axis light beam passing area in compact designs
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively addresses vignetting issues, enabling the formation of a well-defined blurred image for all angles of view, improving imaging performance by ensuring proper light distribution and reducing edge emphasis in the periphery.
Implementation Method 1
the apodization filter is a transmittance distribution filter in which a transmitting light quantity decreases as a distance from an optical axis increases
Data Source
AI summary
An image pickup optical system includes an aperture stop, a first apodization filter disposed on an object side of the aperture stop, and a second apodization filter disposed on an image plane side of the aperture stop, each of the first apodization filter and the second apodization filter satisfies a predetermined condition, and a meridional light beam of a maximum angle of view has an optical path not involving at least one of a point of intersection between the optical axis and the first apodization filter and a point of intersection between the optical axis and the second apodization filter when an aperture size of the aperture stop is maximum.